1. Field of the Invention
This invention relates to otic prostheses; more particularly to an improved stapedial prosthesis.
2. Description of the Prior Art
Reconstruction of the sound-conducting mechanism of the middle ear by surgical implantation of biocompatible prostheses is well-known. FIG. 1 of the drawings is a schematic representation of the natural mechanism for transmitting vibrations of the eardrum (tympanum) to the sound-producing organs of the inner ear which are located behind the aperature (oval window) between the middle and inner ears. The mechanism includes three tiny bones called the malleus, the incus and the stapes, which move in response to the vibration of the tympanum. The stapes, in particular, extends from the lenticular process of the incus to the oval window and moves in piston-like fashion to transmit sound vibrations from the incus to the oval window.
When the stapes becomes diseased, it may be removed and a stapedial prosthesis may be implanted in its place, all by well-known surgical techniques. One of the most widely-used stapedial prostheses is a piston-like member formed of stainless steel, "Teflon" (a registered trademark of DuPont for a tetrafluoroethylene-hexa-florapropylene copolymer), polyethylene or other biocompatible material. Such prostheses are illustrated in U.S. Pat. Nos. 3,196,462; 3,711,869; and 3,931,684, for example and typically include a bucket (or socket) at one end for receiving a portion of the lenticular process of the incus and a cylindrical rod portion at the other end for engaging the oval window (or a vein graft positioned thereover by the surgeon).
A problem associated with stapedial prostheses of this type is providing means for quickly and predictably securing the bucket end of the prosthesis to the lenticular process of the incus in a manner to (i) avoid the occurrence of pressure necrosis, which may result from the securement being too tight and (ii) prevent loosening of the securement, which may result in the prosthesis becoming dislodged after implantation and thereafter extruding within the middle ear. U.S. Pat. Nos. 3,711,869 and 3,931,648 address this problem and provide certain alternatives to the use of a wire bail as the means of securement disclosed in U.S. Pat. No. 3,196,462. The wire bail prosthesis offers certain advantages in stapedial replacement surgery, however, primarily the ease with which the prosthesis may be introduced; therefore, persons skilled in the art would like to continue to use the bail-and-bucket prosthesis if the above-mentioned problems could be overcome.
The bail, (or handle) of a bail-and-bucket, piston-type prosthesis is oriented by the surgeon so that its axis of pivotal rotation generally is horizontal. With the prosthesis in that orientation, the bail is rotated in an upward arc, past the horizontal, until the bail contacts the long process of the incus. Only the frictional engagement of the bail against the incus holds the bail in place. If the bail should rotate downwardly, out of range of contact with the incus, the prosthesis may become dislodged and extrusion may result.